Electrical generators may be used in many different fields. When a generator is e.g. used in a wind turbine, one of the more important economic parameters, with respect to the dimensioning of the wind turbine, is the size of the housing. It is therefore of great importance to be able to minimize the diameter of the wind turbine. In order to minimize the housing one has to minimize the gearbox/gear wheel connecting the wing and the generator. This can be achieved by providing a generator that has a relatively large effect per revolution.
One way to achieve this is to have a generator with as small a radial extent as possible, since the generator occupies a relative large amount of space in the housing of the wind turbine.
Another aspect to be considered when implementing generators in wind turbines is that the generator has to be effective both at a low and a high number of revolutions.
An electrical machine based on a conventional radial flux generator (see FIG. 1) is most frequently used.
A main problem with generators of this kind in certain situations is that the diameter for a given power output is relatively large, because of the radially built stator construction.
A further disadvantage is that the stator surrounds/encircles the rotor, thereby adding to the diameter of the generator.
Another disadvantage is the relative low induction in the air gap caused by the individual arrangement of the material between the recess (7) and the recess (2) themselves, since only the material (7) carries the flux and only covers about 50% of the free space toward the gap.
A further disadvantage is the use of coil material which serves no other purpose than connecting the wound coils (3) located in the recess (2).
Another disadvantage is the complex procedure performed in connection with the insertion of the coils (3) through the narrow openings in the recess (2).
There are many generators of similar kind which are optimized in one way or another, but they all have a radial flux and thus involve the same problem, i.e. a relatively larger diameter, like the one described above.